The presently disclosed embodiment relates to a torch flame resistant shield used in aeronautics to protect the immediate surroundings of engine combustion chambers. It also relates to an aircraft engine nacelle equipped with such a flame resistant shield.
It is known to use a flame resistant shield to protect the vital parts of an aircraft, such as the kerosene supply and the hydraulic and electrical ducts, which are at risk of exposure to torch flames. This flame resistant shield is generally placed on the engine pylons of an aircraft, the engine being a gas turbine engine or the like.
A torch flame corresponds to an accidental leak of combustion gas out of the combustion chamber. The gases are typically at high temperatures, close to 1600° C., and at a pressure of several tens of bars. This temperature is high enough to cause damage to the surrounding vital parts.
Since this flame resistant shield must withstand an accidental exposure to a torch flame, the specifications for this type of shield are consequently very strict:
gas temperature of 1650° C., the gas being certainly oxidizing,
pressure of 37 bar at the source of the flame,
distance of 120 mm from the shield to the source of the flame,
flame diameter of 25.4 mm at the source,
3 minutes' exposure time, during which the shield must not allow the flame through, its opposite face from the flame having to remain at a temperature that is not too high.
Moreover, the flame resistant shield must be able to withstand, under normal operating conditions, an extreme environment and thus tolerate temperatures of the order of 400° C.
It must also be as compact as possible, that is to say with a thickness typically less than 6 mm, while having as little mass as possible for applications in the field of aeronautics.
The flame resistant shield of the prior art typically consists of a firewall made of tantalum which has been treated against oxidation, of thermal insulators based on ceramic fibers, in particular asbestos, impregnated with resin such as a phenolic resin, and possibly a support.
The tantalum layer has a thickness of the order of 0.4 mm whereas the asbestos layer has a thickness of 3.18 mm.
However, these flame resistant shields cannot guarantee continuous integrity at 300° C. as there is currently no organic resin which does not decompose when exposed to such temperatures.
Moreover, it is observed that these flame resistant shields of the prior art age rapidly, which necessitates more frequent and costly replacements.
When removing such a flame resistant shield, which has been in service for a fair while, it can be observed that the binder has disappeared.
As the asbestos fibers have lost their binder, they turn to dust during removal.
Dealing with these shields therefore causes environmental problems due to the extremely harmful nature of the asbestos particles which can thus be dispersed.
Such a flame resistant shield is obviously no longer able to protect the vital parts of the aircraft.